The Sigma 24-70mm f3.5-5.6 HF is one of several products to be introduced at PMA 2001 by Sigma Corporation of Japan. This lens covers focal lengths from 24mm super-wide-angle to medium telephoto. It employs Hellical Focusing system (HF) for focus adjustment, which allows straight movement of front lens elements. Thus the front of the lens does not rotate it allowing the use of a "perfect hood" and the easy use of polarizing filters. Minimum focusing distance from the film plane to subject at all focal lengths is 15.7inch (40cm). It incorporates aspherical lens to minimize distortion, spherical aberration and astigmatism, resulting in high image contrast and resolution. The lens also features a depth of field scale that serves for determining the subject's depth of field at a specific focal length and distance. The lens materials used in this lens are lead and arsenic free ecological glass.